1. Related Technical Fields
Related technical fields include map information guidance devices, map information guidance methods, and computer programs which perform map guidance.
2. Related Art
Recently, navigation devices that perform vehicle travel guidance so that a driver can reach a desired destination easily are often installed in vehicles. Here, a navigation device is a device which is capable of detecting the current position of a vehicle using a GPS receiver or the like, obtaining map information corresponding to the current position from a storage medium such as a DVD-ROM or an HDD, or through a network, and displaying the obtained map information on a liquid crystal monitor. The map information including the current position of the vehicle are read from the storage medium or the like, and on the basis of the map information, a map image of the periphery of the current vehicle position is drawn and displayed on a display device. At the same time, a vehicle position mark is superposed on the map image, and as the vehicle moves, the map image is scrolled, or the map image is fixed on the screen and the vehicle position mark is moved. Thus, the current location of the vehicle can be learned at a glance. In recent years, cellular telephones, personal digital assistants (PDAs), personal computers and the like often have a function similar to the navigation device above.
Throughout Japan, new roads are constructed every year. At the same time, existing roads are destroyed and the shape of existing roads is modified. In this case, a problem arises in that information relating to new roads and the like constructed after the map information of the navigation device or the like have been generated is not recorded in the map information. In other words, in a navigation device or the like storing map information that does not include new roads and the like, the new roads are not displayed on the liquid crystal monitor, and since the new roads are not included in route searches, the navigation device finds recommended routes that do not pass along the new roads. Consequently, it may not be possible to find the optimum route. To avoid this problem, the map information stored in the navigation device or the like must be updated at intervals of a certain time period. Here, map information updating is performed by purchasing a storage medium having new map information and replacing the old storage medium with the new storage medium, or overwriting the map information in the navigation device or the like on the basis of map information for updating (hereinafter referred to as map update information) that is distributed from a map distribution center or the like.
Here, the method of updating the map information in the navigation device or the like using the map update information distributed from the map distribution center is advantageous because it does not require a storage medium during the update operation, and map updating can be performed at an earlier timing. For example, Japanese Patent Application Publication No. JP-A-2004-85245 (pages 6 and 7, FIG. 3) describes art that confirms with a map distribution center whether there is a map information update for a guidance route when a route search to a destination is performed. If there is a map information update, map update information is acquired from the map distribution center and used to update the map information.